1 Piece Oil Pan Gasket Leak at Rear

[adf5565]

I installed a Summit Racing cast aluminum pan along with a FelPro 1 piece gasket on my freshly rebuilt 350. I purchased the gasket on LMC but I believe it is the FEL-OS34509T, which is thin front seal. My timing cover is a cast aluminum one which states it requires the thin front.

Everything is good initially but about 30 seconds after startup I get a fairly significant leak from the rear of the pan. Then strangely after about 2-3 minutes as the engine warms up, the leak will stop. I made sure everything was torqued properly but no change. It repeats this every time during cold-cold ish startup.

I dropped the pan today and it seems the rear of the gasket wasn’t as tight as it should be, but the gasket seemed to be installed properly.

The front of the pan and sides seal fine and don’t leak, just the rear. Anyone have any thoughts? I am going to order another 1 piece gasket in case I got a dud but I am definitely stumped.

[HO455]

I would set the pan on the block without a gasket(s) and check how close it fits to the block.

[adf5565]

Engine is still in the truck with the flywheel on but I will try it and hopefully can see enough. How close is it supposed to be?

[HO455]

The side flanges should be flat on the block with no gaps or warping that allows the pan to rock.

The ends will have clearance you can check by putting modeling clay in place of the gasket and snugging the 4 corner bolts down then remove the pan and inspect the clay for uniform depth.

[Chaparralman1974]

I went through 4 of those crappy 1 piece blue junk gaskets and they leaked in the rear just like yours! I tried 2 different oil pans....still leaked in the rear. I went back to the tried and true cork and rubber setup and now I have no leaks at all. I know that some folks swear by them, but I will never use one again.


Clay